Lately, I’ve been concerned about a trend I've noticed on Puffer-keeping forums:
Aquarists purchase an additional Puffer to prevent the first Puffer that they
own from “getting lonely”. In this article, I hope to explain why this is
unnecessary, and may even be hazardous for your Puffers.

Many fish species throughout the world school or shoal for protection from
predators. By staying together in large numbers, these fish are able to reduce
the chances of becoming a meal. Sometimes, young Puffers are found in
large groups. However, as they mature these Puffers usually go their separate
ways. From this point on, Puffers begin to live a solitary life where
interaction with conspecifics is usually limited to mating season and the
occasional territorial dispute. There is a very logical reason for this--Puffers
are predators! As predators, they spend many hours cruising their territory
searching for food. It may be many hours between meals, and if they find an area
that is rich with food, they are not going to want another Puffer eating what
could be their last meal for days. This is why Puffers declare territory
as their own and will occasionally fight to the death to defend it.

In the aquarium,
territory is at a premium. Compared to the rivers, estuaries and open oceans
that puffers inhabit in the wild, the aquarium is a very small environment. As a
territorial family, Puffers require space to call their own. Introducing more
than one Puffer into a tank, especially a tank that is too small, is asking for
problems. If two Puffers cannot establish clear territories, they will often
fight. Depending on species, some will not stop until they kill the other
Puffer. After purchasing several puffers, many people will talk about how well
the Puffers get along and seem to be best friends. Unfortunately, most
newly-purchased Puffers are still very young - probably under a year old. This
means they are still immature and focused on surviving into adulthood more than
anything else. As they age and mature these “buddies” often start to define
territories and if enough space is not provided, they will start to fight over
the given space. With some species, such as Tetraodon lineatus, this fighting
usually leads to one badly injured Puffer and another dead Puffer. So, as
solitary fish that need space, Puffers do not need tankmates.

Perhaps some other fish can live with the Puffer? Well, this really depends on
the Puffer species. When it comes to piscivorious Puffers (those whose primary
diet is fish), cohabitation with another fish is a death sentence. These Puffers
will ambush and kill any tankmates, even those who are much larger than the
Puffers themselves! The molluscivores (Puffers who primarily eat
crustaceans) may accept tankmates. Some may accept them for life. Others will
tolerate tankmates for a while, then one day decide that they want to see how
they taste! So, while some Puffers may tolerate other fish, it is best for them
to either be kept alone or in a species tank.

Anyone who has kept a Puffer knows that they are not the fastest swimmers in the
world. They float around more like a blimp than a torpedo. What does this have
to do with keeping them with tankmates? It presents a problem during feeding
time. Fish that move much faster than Puffers are often able to consume the
majority of the food before Puffers are able to get their share. This is
especially true for some of the smaller Puffers, such as C. travancoricus (Dwarf
Puffers). To compensate for this inequality in feeding, owners will often
overfeed the fish in order to allow the Puffers to get enough to eat. The result
is an excessive nutrient load in the aquarium from leftover food rotting in the
tank. This situation can lead to algae problems, or even a crash of the tank,
and could kill the inhabitants.

It is a common thing for Puffer keepers to give the animals human
characteristics. Unlike people, Puffers do not need friends or companions for
their well-being. They will not get lonely nor will they become depressed
because they do not have another Puffer around. In many cases, quite the
opposite is true, and they can be much more personable to their keeper if kept
as individuals. As a general rule, most Puffers will live a healthier, happier,
less stressful life if there are no other Puffers in their territory.

As with any rule, however, there are always exceptions, and this one has a few.
While most species of Puffers do best alone, there are a few that will tolerate
tankmates. This article needs to be prefaced with a disclaimer: “Puffers, as a
species, are individualistic - and while one Puffer may get along with
tankmates, a different Puffer of the same species could be completely intolerant
of anything else in their tank.” For this reason, if you decide to keep multiple
Puffers in the same tank, you should have an alternate tank available just in
case things don't work out.

C. travancoricus, the dwarf
puffer. Photo by author.

The first exception is the popular Dwarf Puffer (Carinotetraodon
travancoricus). This Puffer stays small, only reaching 1-1.5 inches. One
thing that makes these Puffers unique is that it is easy to determine their
gender once they have sexually matured. The males stay smaller and develop a
dark brown vertical stripe on their stomachs. Females are usually larger and
lack the stripe. If the proper tank is provided (that is, one that supplies at
least 2-3 gallons per Puffer), is heavily decorated and has more hideouts than
there are Puffers, then keeping 2 or 3 females to one male often works well. In
fact, under these circumstances and with proper diet, Dwarf Puffers will often
spawn. Dwarf puffers have been kept successfully with Otocinclus algae
eaters. There has also been limited success in keeping Dwarf Puffers with
different species of shrimps, such as Amano, Cherry or Ghost shrimp. There is
always a risk with shrimp that some Dwarf Puffers will decide that they are food
and will eat them.

Another freshwater Puffer that has been kept with conspecifics successfully is
the South American Puffer (Colomesus asellus). In large tanks, at least
55 gallons, South American Puffers can be kept in small groups. As with any
Puffer, the tank needs to be heavily decorated. The decorations should be set up
so that they break up the sight lines in the tank to minimize confrontations.
Also, there should be more caves or hiding spots than Puffers in the tank, to
prevent them from fighting over a place to sleep or rest.

Tetradon biocellatus not
only do best when kept alone, they are actually a threat to tankmates!
Photo by Robert Fenner.

Tetraodon biocellatus
or the Figure Eight Puffer, tends to live longest when kept as individuals. A
study done on keeping Figure Eights demonstrated that individuals live much
longer than those housed together. The oldest individual in the study lived more
than 18 years! However, they have been kept with Bumblebee Gobies (Brachygobius
nunas). These Gobies stay very small and generally keep to themselves. They
are also excellent scavengers and do a good job of cleaning up the mess that the
Puffers often create when eating. Figure Eight Puffers and Bumblebee Gobies are
a good mix because they have very similar environmental requirements. Both will
do best in lightly brackish water with a specific gravity around 1.005. It must
be noted that occasionally, especially in a tank that is under-decorated, Figure
Eights will decide to taste their Goby tankmates.

T. fluviatilis will often get along
with T. nigroviridis, as long as the smallest specimens possible
are purchased. T. fluviatilis pictured here. Photo by
author.

The Green-Spotted Puffer (Tetraodon nigroviridis) and the Ceylon Puffer (Tetraodon
fluviatilis) are other exceptions. When given the proper environment, these
two species will often cohabitate without a problem. Often, multiples of the two
species can be kept together as well. As a reminder, for this to work well, the
tank must be well decorated, with plenty of hiding places and lots of space. For
these larger Puffers, they need at least 30 gallons per Puffer. If kept in
anything smaller, there is a much greater risk of fighting and territorial
issues.

There are several
things to consider when keeping multiple Puffers of the above species in the
same tank. First, always add Puffers of the youngest age and smallest possible
equal size. Young Puffers tolerate each other better and are more likely to get
along throughout their lives. Second, always add them at the same time. Adding a
new Puffer to an established Puffer tank is a sure way to get the Puffers to
fight, and possibly kill each other. If the need should ever arise to add a
Puffer to an established tank, the best way to do it is to remove the
established puffer, redecorate the entire tank and then reintroduce both
Puffers. Unfortunately, even this may not be enough. For this reason and simply
because Puffers are so unpredictable, alternative housing arrangements should
always be available.

While all of these Puffers have been kept together with either conspecifics or
other fish, it is always a risk keeping them together. These fish are, first and
foremost, predators- and that instinct will never go away. Always have a
spare tank ready to go in case things begin to go bad. Minor disputes between
new tankmates are completely normal as they set up territory and adjust to the
captive environment. Should the fighting continue for a prolonged time or become
worse, the Puffers should immediately be separated to prevent any permanent
damage or death.

I hope that this article helps to dispel a few of the common misconceptions
present in the hobby regarding Puffers’ social habits. Please feel free to email
me if you have any further questions on this topic.